text: Iodides (including sodium iodide) are detectably oxidized by atmospheric oxygen (O) to molecular iodine (I). I and I complex to form the triiodide complex, which has a yellow color, unlike the white color of sodium iodide. Water accelerates the oxidation process, and iodide can also produce I by photooxidation, therefore for maximum stability sodium iodide should be stored under dark, low temperature, low humidity  conditions.